1. Field of the Invention
This invention relates to the sizing of textile yarns, and more particularly to melt sizing with compositions later removable by aqueous means.
2. Description of the Prior Art
The art of textile sizing contains many examples of solutions and dispersions of sizes in water and/or organic solvents. Such compositions inevitably require a slow and expensive drying step after application to yarns. A few examples are known of melt sizes, which do not require removal of solvent, these sizes being based in general upon waxes and other water-insolubles. U.S. Pat. No. 3,466,717 is directed to the application of such a wax-based melt size, removable only by nonaqueous solvents after processing. Besides this restriction, wax sizes have the futher deficiency that they lack the film strength, adhesion, flexibility, and ready variability and control of melt viscosity which are inherent in the tougher polymer-based melt sizes of the present invention.
Polymers high enough in molecular weight to be good film formers generally give melts having excessively high viscosities and slow solidification rates. Such polymers, if applied as melt sizes, would therefore be expected to flow poorly onto and throughout the fibers of a yarn, and to require application of excessive cooling means and times for solidification.
U.S. Pat. No. 4,082,883 relates to the intimate combination of a film-forming thermoplastic polymer and a melt-compatible non-polymeric solid modifier, which is said to be readily meltable, quick-setting, essentially water or alkali soluble, and thus capable of melt application to and extraction by aqueous solvents from textile filaments, yarns and fabrics. The melt modifiers are said to reduce the viscosity of the polymer melt and at the same time to effect an increase in the setting rate. This patent suggests a wide range of suitable thermoplastic polymers which may be used, including various copolyesters, acrylic and methacrylic acid copolymers, vinyl acetate copolymers, phosphonate copolymers, etc. Example 19 relates to the use of 40 g of a terpolymer of 56% ethyl acrylate, 33% methyl methacrylate and 11% methacrylic acid, modified with 60 g of adipic acid. A melt made with 60% polymer and 40% adipic acid was too viscous to be effectively applied to yarn. The present invention provides a composition which includes no greater than about 5% of a particular acid modifier, and includes acrylic acid rather than methacrylic acid in the terpolymer. The composition according to this invention containing very small amounts of acid modifier is very desirable because it is essentially smokeless and odorless. Also, use of acrylic acid rather than methacrylic acid provides advantages such as ready polymerization of the terpolymer, reactivity ratios of the monomers are closer, and the glass transition temperature is maintained at a low level.